Pacemakers offer a chance to reduce syncope in selected patients who have a neurally mediated form of the condition, researchers found.

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This study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

This study found that the use of a subcutaneous loop recorder identified patients with neurally mediated syncope, allowing clinicians to then reduce the patients' recurrence of fainting by using pacemaker therapy.

Note that one out of three pacemaker patients will benefit from pacing therapy within the subsequent two years.

CHICAGO -- The use of a subcutaneous loop recorder identified patients with neurally mediated syncope, allowing clinicians to then reduce the patients' recurrence of fainting by using pacemaker therapy, researchers reported here.

Of the 77 patients randomized to having their pacemakers turned on or off, 57% in the "off" group had a recurrence of syncope within 2 years compared with 25% of those in the "on" group, Michele Brignole, MD, of Ospedali del Tigullio in Lavagna, Italy, reported in a late-breaking clinical trial here at the American College of Cardiology meeting.

Essentially, one out of three pacemaker patients with syncope will benefit from pacing therapy within the subsequent two years, Brignole said. "No therapy has proven effective for these patients. Now we have shown that cardiac pacing works in this highly selected population."

Neurocardiogenic syncope is categorized as vasodepressor, which is mostly hypotensive; cardioinhibitory, which is mostly bradycardia; or mixed.

Brignole said that more than a million people worldwide have syncope: about 10% with a cardiac cause, 50% with a non-cardiac cause, and 40% with an unknown cause.

"Reflex syncope is benign regarding mortality, but it increases the risk of secondary trauma and impacts negatively on patient quality of life," he told MedPage Today.

The patients in this study, called ISSUE-3 (Study on Syncope of Uncertain Etiology 3), had their asystole neurally-mediated syncope (NMS) identified via a subcutaneous loop recorder (previous studies had used tilt testing). The asystole episode, or pause, had to last greater than 3 seconds. The average time was 11 seconds, which was much longer than the pause length used in previous studies, Brignole said.

He suggested that part of the reason for the success of the pacing therapy was careful patient selection, including having a longer asystole episode, older age, and with more severe episodes. Patients with non-syncopal asystole greater than 6 seconds also were eligible for the study.

Other randomized studies that did not show a positive effect for pacemaker therapy in syncope patients did not specifically look at asystole NMS. Also, these studies included younger patients, which may have contributed to the negative results, he said.

ISSUE-3, a randomized, double-blind controlled study, enrolled patients from 51 centers in Western Europe and Canada who were over 40 years-old and whose symptoms had been ongoing for more than eight years. Of the 511 patients who met the inclusion criteria, the loop recorder identified 77 with asystole NMS.

"Dual-chamber pacemakers with a hysteresis feature have been proven to be better than single-chamber pacemakers," Brignole said.

The mean age of patients in both groups was 63. There were more men in the activated group (53%) and more women in the inactivated group (59%).

Brignole said that there is no known difference in treatment outcomes between men and women.

About half of all patients had hypertension, 10% had diabetes, and 11% had structural heart disease. The mean age of the first episode for both groups was 46.

The primary endpoint was the time to first syncope recurrence. However, Brignole said a better endpoint would have been syncope burden. The ISSUE-3 investigators chose time to first recurrence so they could compare their results with the previous two ISSUE trials.

There were five procedure-related complications: two right atrium lead dislodgements, two right ventricle lead dislodgements, and one subclavian vein thrombosis.

"The observed 32% absolute and 57% relative syncope reduction rate support the use of this invasive treatment for the relatively benign NMS," Brignole concluded.

He added that the overall strategy of using an "implantable loop recorder in order to determine indication for pacing likely contributed to the positive findings and explains the discrepancy with the negative results of some previous reports."

He also said he hopes these findings will be considered for future updates to current guidelines for these patients.

In the U.S., pacemaker implantation is not an approved indication for patients with syncope.

The study was funded by Medtronic.

Brignole reported he had no conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, Nurse Planner

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